The invention relates generally to data storage systems and, more particularly, to disk based data storage systems.
A disk drive uses a transducer to write data to and read data from the tracks of a data storage disk. Traditionally, transducers have included a single read/write element for performing both read and write operations on a disk surface. More recently, dual element transducers that include separate elements for performing read and write operations have become popular. For example, a common dual element head arrangement includes a magneto-resistive (MR) read element and an inductive write element within a single transducer package. Other dual element transducer configurations are also possible.
Dual element transducers typically have a lateral offset between the read and write elements of the transducer when the transducer is positioned above a target track. The lateral offset is usually the result of both the physical geometry of the transducer and the skew angle caused by the rotary actuator. Because the skew angle changes from track to track, the lateral offset for the transducer generally changes as the transducer is moved across the disk surface. Because of the lateral offset between the read and write elements, microjogging is generally used during read and/or write operations to accurately position a corresponding element of the transducer with respect to the track. Without microjogging, the disk drive servo controller acts to center the read element of the transducer about the track centerline. Microjogging is used to move the transducer a small lateral distance away from this centered read element position to appropriately align the head for performing a data transfer operation. For example, if data is to be written in a centered position on the track, microjogging is used to position the head so that the write element is centered about the track centerline. This requires a microjog distance equal to the lateral offset between the read and write elements. Microjogging is typically performed by injecting an offset value into a track following servo control loop.
There are many instances during disk drive operation when it is desirable to move data from one portion of a track to another portion of the same track. For example, this may be required when performing functions such as reassign verification, error recovery, background flaw scanning, and power safe operations (e.g., a power safe read/modify/write operation). Traditionally, the movement of data within a single track was performed by (1) positioning the transducer in a xe2x80x9creadxe2x80x9d position above the desired track, (2) reading the data to be moved from the original location on the track, (3) microjogging the transducer to a xe2x80x9cwritexe2x80x9d position above the track, and then (4) writing the data to the new location on the track. However, because the microjog operation took a finite amount of time to perform, the transducer was commonly past the beginning of the new location on the track by the time the microjog was complete. Thus, a full revolution of the disk was required before the write operation could be performed. As can be appreciated, this revolution of the disk takes time and degrades the overall performance of the drive.
Therefore, there is a need for a method and apparatus for moving data within a single track of a disk that is more efficient the past techniques. Preferably, the method and apparatus will reduce or eliminate the need to wait for a full revolution of the disk before data can be written to the track of the disk.
The present invention relates to a disk drive system that is capable of efficiently moving data from one location to another within a single track of a data storage disk. To accomplish this, the system stores user data at multiple different offset positions within a single track. That is, some of the data sectors stored within a track are written at a standard lateral write position within the track and others are written in a position that is offset from the standard position. In one embodiment, for example, some of the data sectors in a track are written in a centered position on the track while others are written at a predetermined off-track position. Preferably, the lateral distance between the standard write position and the offset position is equal to the lateral offset between the read and write elements of the dual element transducer for that particular track. Thus, data can be read from one portion of the track and then written to another portion of the track (i.e., an offset location) without performing a microjog operation. Because the microjog does not have to be performed, there is no delay in performing the subsequent write operation and a wasted revolution of the disk is rarely, if ever, required.